Thin film transistors have advantages such as high mobility, good stability, simplicity of manufacturing process and so on. Oxide semiconductor materials, represented by indium gallium zinc oxide (IGZO), are widely applied in fields such as thin film transistor liquid crystal displays (TFT-LCDs), active matrix organic light-emitting diodes displays (AMOLEDs), e-paper displays, integrated circuits and so on.
Capacitance generated between the gate electrode and the source electrode of an oxide thin film transistor is small so as to make a display panel have advantages such as high resolution, low power consumption and the like. Top-gate oxide thin film transistors play an essential role in large-sized displays and can greatly enhance the electrical performance of thin film transistors, such as stability and uniformity of thin film transistors.